1. Field of the Invention
The present invention relates to a transmitted picture quality monitoring apparatus and more particularly, to a transmitted picture quality monitoring apparatus for monitoring the transmitted picture quality on a transmission chain that includes a format converter, from a remote place by extracting the picture quality characteristic amount of a picture at each point of the transmission link and comparing the extracted picture quality characteristic amount.
2. Description of the Related Art
When monitoring the picture quality on a transmission chain, the picture quality characteristic amount of pictures at any point is extracted and the extracted picture quality characteristic amount are transmitted to a central control center and compared so as to monitor the transmitted picture quality on a transmission link in batch.
This inventor et al. have proposed a calculation method for the picture quality characteristic amount for monitoring the transmitted picture quality on a transmission link through patent documents 1, 2. According to this calculation method of the picture quality characteristic amount, a picture is divided to blocks each having a certain size and the picture of each block is orthogonally transformed so as to extract a transformation coefficient and the extracted transformation coefficient is transmitted to a central control center. This calculation method of the picture quality characteristic amount exerts its effect when as described in the patent documents 1, 2, spread spectrum is applied to a picture and then that picture is orthogonally transformed and the transformation coefficient is extracted and transmitted. The spread spectrum is realized by changing the sign of each pixel constituting a picture at random.    Patent document: Japanese Patent Application Laid-Open No. 2003-9186    Patent document: Japanese Patent Application Laid-Open No. 2003-87823
According to the inventions proposed in the patent documents 1, 2, deterioration in signal-to-noise ratio of a received picture due to coding noise and transmission errors in a transmission link can be estimated accurately.
However, if a format converter is included in a transmission chain and a picture is converted in terms of format halfway of the transmission link and transmitted, the number of lines constituting a screen, the number of fields or frames per second or the number of horizontal pixels are converted by a format converter.
The inventions proposed by the patent documents 1, 2 employ common ways of monitoring the quality of transmitted picture quality on a transmission link by comparing pictures on transmission side and reception side and for this comparison, estimating a mean square error (MSE) of a differential of each of pixels constituting a picture. This way presumes that the formats (number of scanning lines, number of fields, number of frames, and number of horizontal pixels) before and after transmission are matched with each other as understood from a fact that the differential of each pixel is obtained.
That is, because the inventions proposed by the patent documents 1, 2 presume that the format of a picture at each point of the transmission link is identical, if the format of a picture is converted halfway of the transmission link, pictures before and after the transformation of the format can not be compared with each other.
For example, in case where pictures are transmitted between Europe and Japan, the picture in Europe is based on the 625/50 format in which the number of the scanning lines (vertical lines) in a frame is 625 while the number of fields per second is 50 (the quantity of frames is 25). On the other hand, the picture in Japan is based on the 525/60 format in which the number of the scanning lines (vertical lines) in a frame is 525 while the number of fields per second is 60 (the number of frames is 30). The number of the horizontal pixels in the both formats are the same.
Because for transmission between countries with different picture formats, the format is converted during the transmission, there is left such a problem that the transmitted picture quality on a transmission link cannot be monitored from a remote place.